Canadian Policy Wiki:Template substitution
This page lists templates that should always be subst'd except in the Canadian Policy Wiki namespace. About subst Definition : The subst: keyword (short for "substitution") is used as a prefix inside a template code. It changes the way the software expands the template. Ordinarily, a template is expanded "on the fly"; that is, the template code calls a separate page for the text every time someone edits a page it's used on. Placing "subst:" inside the curly brackets tells the software to permanently substitute the template with text of the template (that is, the text that is on the template's article page). Therefore becomes and the full text is expanded when you save the page. Usage Note: Template substitution is a permanent change that removes functionality, it should generally be avoided without a good reason. : You can subst a template tag by adding "subst:" to a template tag. For example, use instead of . When this is a major component of an edit, it is strongly suggested that the template be mentioned in the edit summary (for instance, put " " or "test1 applied" in your edit summary so other editors can easily see what you have done). Arguments for substitution * Templates are often modified or deleted. If a template is boilerplate text, consider whether you want it to vary as the template is improved. If your answer is "no", substitution is warranted. An example of this is the template. The archives of a user's talk page should show the actual welcome message they received, not the current welcome message. * If there is a template you would like to modify for a single occasion, but you don't want to modify the template for all the pages that use it, and you don't want to make a new template, you can substitute the template and then with a second edit, make the modifications. For example: a template might be used with all the states in the United States and the District of Columbia. The template might be worded correctly for the states, but not for DC. To fix the wording, you can substitute the template and then fix the wording. * Substituting en masse may speed up the site, though the amount and significance of this is the subject of frequent debate. Every time someone views a page, the server must get text from a separate page for every template used. Although each individual template has little effect, the vast number of templates used on Wikipedia is one factor affecting server load and article load times. * Templates are a prime target for vandalism. Changes made to a single template are propagated to every article where the template is used. In this way, a single edit can vandalise thousands of individual pages, though this is as easily reverted as any other vandalism. In the past, widely-used templates that were vandalized were usually reverted within a minute. Substituting prevents this type of attack, assuming a good version is substituted, since the template is converted into real text and will no longer be updated. If the template is substituted while in a vandalized state, however (e.g., by bots enforcing this page), the vandalism is much more difficult to clean up, which makes this a disadvantage. Protection of high-risk templates is an alternate solution. This does not appear to be a significant problem as most vandals are not very sophisticated in their methods. * Using templates helps hide wikitext from newcomers. (Of course, there is a "how to edit" link at the bottom of each edit page.) : See Wikipedia:Transclusion costs and benefits for further details.